I. INTRODUCTION
Power divider has been widely used in many microwave and millimeter-wave systems as a key element in multiplexer, coupler and antenna feeding system. Recently, various power dividers have been presented and developed [Reference Song and Xue1–Reference Chau and Hsu18]. These designs include: ring-cavity power dividers [Reference Song and Xue1], radial waveguide power dividers [Reference Hong, Kimball, Asbeck, Yook and Larson2–Reference Song, Zhang, Hu and Fan6], conical power dividers [Reference De Villiers, Vanderwalt and Meyer7], rectangular waveguide power dividers [Reference Cheng, Jia, Rensch and York8, Reference Becker and Oudghiri9], coaxial waveguide power dividers [Reference Song and Xue10–Reference Jia, Chen, Alexanian and York14], and microstrip line and slotline power divider [Reference Song and Xue15–Reference Chau and Hsu18]. Conventional rectangular waveguide components have been widely used in low loss and high-power microwave, and millimeter-wave communication systems [Reference Song and Xue1–Reference Jia, Chen, Alexanian and York14]. However, they cannot often satisfy the size and cost requirement of current low-cost highly integrated communication systems. In addition, it is difficult to be integrated with other microwave and millimeter-wave planar circuits (e.g. microstrip, slotline, coplanar waveguide, etc.). In [Reference Song and Xue15–Reference Chau and Hsu18], microstrip and slotline power divider were presented; good in-band power splitting, impedance matching, isolation, amplitude, and phase balance, and out-of-band rejection are obtained both in simulations and measurements.
In recent years, a new technique, substrate-integrated waveguide (SIW) has been constructed by two parallel rows of via holes in a metalized planar substrate. The SIW is realized by metallic via arrays, which shows the similar propagation characteristics of conventional rectangular waveguide. It has merits of low-cost, low-profile, and easy integration with planar circuits [Reference Kumar, Jadhav and Ranade19].
Several power dividers/combiners based on SIW technology have been investigated and designed [Reference Song, Fan and Zhang20–Reference Song and Fan27]. Among these SIW power dividers [Reference Song, Fan and Zhang20–Reference Song, Fan and Zhang22], they show disadvantage of narrow operation bandwidth due to the resonant nature of their configurations. In [Reference Song and Fan27], a broadband in-phase power divider was demonstrated with the used of voltage probe (dual-disc) to achieve broadband input impedance matching, where 10 dB return loss bandwidth of about 4.4 GHz were achieved. However, the increase in complexity of nowadays millimeter/micrometer-wave systems brings about the need multiple-way out-of-phase passive circuits, which will be of great advantage to enable good connectivity between all interconnects present in the microwave/millimeter-wave systems.
In this paper, an SIW power divider has been presented. This SIW power divider can achieve an arbitrary N-way power-dividing performance in out-of-phase situation. Coaxial dual-disc probe impedance-matching transformer is applied to achieve wider bandwidth performance. A six-way out-of-phase SIW power divider operating at C-band with center frequency of 6.7 GHz is designed and fabricated. The 180° out-of-phase is achieved by changing the polarity of the potential of the output ports (i.e. three of them at the top plane and other three at the bottom plane of the structure). The simulated and measured results show good agreement.
II. DESIGN AND ANALYSIS OF THE SIW POWER DIVIDER
As shown in Fig. 1, a six-way out-of-phase SIW power divider consists of central input coaxial dual-disc probe, six of the SIW-to-microstip transitions; where three of these transitions are situated at the top plane and the other three are at the bottom plane of the structure. The phase difference between two adjacent peripheral ports is 180° out-of-phase thus; the electric field between them is opposite. For symmetry reasons, the six SIW-to-microstrip transitions are identical in shape and size, which can be designed according to [Reference Kumar, Jadhav and Ranade19]. The SIW is a type of dielectric filled substrate with two rows of metallic via to realize electronic walls. With
$$p \leq 2d\comma \;$$
$$d\, \leq \, \lambda _g \, /\, 10\comma \;$$where λ g is the guided wavelength. Almost no leakage will exist along the waveguide. Then, the SIW can be modeled by a conventional rectangular waveguide filled with dielectric material.
Fig. 1. Schematic diagram of the SIW power divider: (a) top view, (b) bottom view.
The out-of-phase SIW power divider is centrally fed using a stepped coaxial line transformer that connects with the central dual-disc probe (Fig. 2). The central dual-disc probe is axially symmetric; which can provide broadband impedance matching from the input coaxial line to the radial line, and can also be processed easily at the substrate. As shown in Fig. 2, the dual-disc probe is as in [Reference Song and Fan27]. So, with a specified coaxial-line input port (e.g. Sub-Miniature-A (SMA) connector), the input admittance of the dual-disc probe in Fig. 2 can be changed by varying c, b, H1, D1, D2, and H2 to be able to achieve a wider bandwidth of the power divider.
Fig. 2. Schematic illustrations of dual-disc parameters.
Parallel structural design approach is adopted in this paper based on its nature, to be able to combine six-way out-of-phase microwave signal in one step. Finally, High Frequency Structure Simulator (HFSS) full-wave tools were used to optimize the dimensions of the central dual-disc probe of Fig. 2.
A) Parametric analysis
Analysis was made on some of the dual-disc probe parameters, to actualize their influence on the performance of the presented power divider structure. Among the parameters, c and H1 parameters were swept and significant effects were observed on the return loss and at the same time the bandwidth of the power divider (see Fig. 3). The sweep was done on the basis of one parameter at a time to recognize independent effect of each parameter on the power divider performances. The values of each parameter are as follows: W = 21.6, d = 0.5, p = 0.8, W1 = 10, L1 = 22.3, W2 = 2.7, a = 1.2, b = 7.2, c = 36.4, e = 4.2, H1 = 1.2, H2 = 0.4, D1 = 26, and D2 = 7.6 mm.
Fig. 3. Dual-disc parameter sweep frequency response: (a) parameter ‘c’, (b) parameter ‘H1’.
III. EXPERIMENTAL RESULTS
A six-way out-of-phase SIW power divider has been designed and fabricated on a substrate of thickness 1 mm and relative dielectric constant of 2.65. The presented power divider was simulated and optimized using the commercial software Ansoft HFSS. The final dimensions of the SIW power divider shown in Figs. 1 and 2 are: W = 21.6, d = 0. 5, p = 0.8, W1 = 10, L1 = 22.3, W2 = 2.7, a = 1.2, b = 7.2, c = 36.4, e = 4.2, H1 = 1.2, H2 = 0.4, D1 = 26, and D2 = 7.6 mm. The photograph of the six-way out-of-phase SIW power divider is shown in Fig. 4.
Fig. 4. Photograph of the fabricated power divider: (a) top view, (b) bottom view.
Figure 5 shows the simulated and measured results of the six-way out-of-phase SIW power divider. Simulated and measured return losses are both greater than 15 dB at frequency range of (6.17–7.62 GHz) and (6.42–7.53 GHz), respectively. Measured average insertion loss of the proposed six-way out-of-phase SIW power divider is about 8.5 dB in the operational frequency range of (5.5–8.5 GHz). To further extend the operating frequency range, the thickness of the SIW can be increased. Compared to the simulated results, the increased insertion loss is mostly likely related to the dielectric loss of substrate and fabrication errors. The simulated and measured 15 dB bandwidth are both 1.45 GHz and 1.11 GHz from (6.17–7.62 GHz) and from (6.42–7.53 GHz), respectively. However, the measured results agree with the simulated ones reasonably.
Fig. 5. Measured and simulated S11 and S21 of the SIW power divider.
Figure 6 depicts the simulated and measured transmissions from central input port to the peripherals output ports, respectively (i.e. Sn1, where n = 2, 3, 4, 5, 6, and 7).
Fig. 6. Measured and simulated transmissions of the SIW power divider.
From Fig. 7, the measured phase difference between the outputs of fabricated power divider; S21, S41, and S61 are in-phase (i.e. ports 2, 4, and 6 are at top plane), S31, S51, and S71 are also in-phase with one another (i.e. ports 3, 5, and 7 are at the bottom plane), and all the top plane ports are out-of-phase with bottom plane ports. Hence, the 180° out-of-phase function of the designed power divider has been achieved.
Fig. 7. Measured ports phase angles of the power divider.
Figure 8 displays the simulated and measured isolations of the power divider, where only port 2 isolations (i.e. S23, S24, S35, S26, and S27) were shown on the figure; as remaining ports isolations are of the same pattern with that of the port 2. From the graph, it can be seen that from frequency of 5.5–8 GHz all the isolations are greater than 8.16 and 9.25 dB for simulated and measured results, respectively. A comparison between this work and other works is given (Table 1).
Fig. 8. Simulated and measured isolations of the SIW power divider.
Table 1. A comparison of this works and other works.
IV. CONCLUSION
A broadband six-way out-of-phase power divider based on SIW technology has been reported. The dual-disc probe was used to achieve broadband impedance matching. The presented power divider was designed, fabricated, and measured. The measured and simulated results show good agreement with each other over the operating frequency range (5.5–8.5 GHz).
ACKNOWLEDGEMENTS
The work for this grant was supported in part by National Natural Science Foundation of China (Grant no 61271026), by the Program for New Century Excellent Talents in University (Grant no NCET-11-0066), and by the project (No: IRT1113) under “Program for Changjiang Scholars and Innovation Team in University”.
Kaijun Song (M’09-SM’12) received the M.S. degree in Radio Physics and the Ph.D. degree in Electromagnetic Field and Microwave Technology from the University of Electronic Science and Technology of China (UESTC), Chengdu, China, in 2005 and 2007, respectively.
Since 2007, he has been with the EHF Key Laboratory of Science, School of Electronic Engineering, UESTC, where he is currently a full Professor. From 2007 to 2008, he was a postdoctoral research fellow with the Montana Tech of the University of Montana, Butte, USA, working on microwave/millimeter-wave circuits and microwave remote sensing technology. From 2008 to 2010, he was a research fellow with the State Key Laboratory of Millimeter Waves of China, Department of Electronic Engineering, City University of Hong Kong, on microwave/millimeter-wave power-combining technology and Ultra-Wideband (UWB) circuits. He was a senior visiting scholar with the State Key Laboratory of Millimeter Waves of China, Department of Electronic Engineering, City University of Hong Kong in November 2012. He has published more than 80 internationally refereed journal papers. His current research fields include microwave and millimeter-wave/THz power-combining technology; UWB circuits and technologies; microwave/millimeter-wave devices, circuits and systems; and microwave remote sensing technologies.
Professor Song is the Reviewer of tens of international journals, including IEEE Transactions and IEEE Letters.
Abdullahi Nura Ahmed received his first degree in Electrical/Electronic Engineering from Bayero University Kano (BUK), Kano, Nigeria in the year 2008. Until now, he is a lecturer III at Jigawa State Institute of Information Technology (JSIIT), Kazaure, Nigeria from 2010.
Now, he is pursuing M.S. degree in electromagnetic field and microwave technology from the University of Electronic Science and Technology of China (UESTC), Chengdu, China, from 2012. His research interests include microwave/millimeter-wave power-dividing technology and microwave/millimeter-wave devices, circuits, and systems.
Fulong Chen is now pursing his M.S. degree in the electromagnetic field and microwave technology from the University of Electronic Science and Technology of China (UESTC), Chengdu, China, from 2012. His research interests include microwave/millimeter-wave power-combining technology and microwave/millimeter-wave devices, circuits and systems.
Bingkun Hu was born in Jiangsu, China in 1990. He received his bachelor of engineering degree in electrical engineering from University of Electronic Science and Technology of China (UESTC) in 2012, and now he is trying to obtain his master degree in electrical engineering in UESTC.
His current research interests include microwave techniques with a focus in RF/microwave components.
Yu Zhu was born in Anhui, China in 1992. He received his bachelor of engineering degree in electrical information engineering from Southeast University Chengxian College in 2014, and now he is trying to obtain his master degree in electrical engineering in University of Electronic Science and Technology of China (UESTC).
His current research interests include millimeter-wave techniques with a focus in RF/microwave passive components.
Yong Fan (M’05) received the B.E. degree from Nanjing University of Science and Technology, Nanjing, Jiangsu, China, in 1985 and the M.S. degree from University of Electronic Science and Technology of China, Chengdu, Sichuan, China, in 1992.
He is now with the School of Electronic Engineering, University of Electronic Science and Technology of China, where he is currently a full Professor. His current research interests include electromagnetic theory, millimetre-wave technology, communication and system. He has authored and co-authored over 130 papers.
Prof. Fan is a senior member of the Chinese Institute of Electronics. He received the first award of science and technology of national industry, the second award of science and technology progress of ministry of electronic industry, the third award of science and technology progress of ministry of information industry, and the third award of science and technology progress of Sichuan province (twice).
